1. Technical Field
This invention relates to a failure judgment system for sensors which detect various data concerning engines.
2. Prior Art
Internal combustion engine for automobiles are often controlled by a microcomputer. Various data concerned with the engine are usually detected and/or controlled by a number of sensors associated with the microcomputer. A failure judgment system for these sensors, which detect various data for accurate control, performs an important role for controlling engines. A plurality of means have been adopted for the of failure thereof judgment. A fail-safe function has been used, which is a function to stop the engine or to perform a change-over control to an alternative standard value for emergency evacuation. This has been triggered by emergencies such as a bad condition of the engine and abnormal overheating of the catalyst which can occur when the control is continued in the same way, using signals outputted abnormally by a failed sensor. The above-mentioned system includes a means to judge the failure of one sensor by combining signals from the other sensors. For example, one system utilizes a failure judgment system to detect failures of the speed sensor in accordance with the output signals of the inlet pipe pressure sensor, the engine speed sensor, and the cooling water temperature sensor, etc. However, failure judgment is done by masking the signals from the monitored sensor and substituting the standard value for emergency evacuation instead of the signals from the monitored sensor. The above-mentioned failure judgment system to detect failures of one sensor by combining the other sensors, however, has a defect in that the judgment can not be reliably executed when a sensor fails, even if only one of the sensors is judged to have failed.
The system that uses the above-mentioned sensors judge failures by using the failure judgment condition combined therefore sometimes misjudge the sensor to be abnormal even if the above-mentioned condition is not actually met, since the combined judgment conditions include the standard value.